The invention relates to membranes having molecular sieve properties and/or catalytic activity and a process for producing the membranes.
Membrane separation technology is a rapidly expanding field. Organic and inorganic materials have been used as membranes in a variety of separation processes, such as microfiltration, ultrafiltration, dialysis, electrodialysis, reverse osmosis and gas permeation. Most membranes have been made from organic polymers with pore sizes ranging from 10 to 1000 angstroms. Membranes have also been made from inorganic materials such as ceramics, metals, clay and glasses.
Synthetic zeolites have been used as adsorptive separating agents for gases or liquids or as catalysts and have usually been sued in the form of granules or pellets often incorporated with a binder such as clay or alumina. The potential of zeolites as components in microporous membranes has not been fully explored.
Zeolites have also been used as components in composite membranes. In such membranes, in addition to the presence of a zeolite phase, the membrane material always contains a second phase with distinctly different chemical composition, physical properties, chemical properties and morphology. As a result of the presence of different phases, the separation properties of composite membranes are determined by the individual properties of the different phases and of the phase boundaries. (Demertzes et al., J. Chem. Soc., Faraday Trans. 1, 82, 3647 (1986)). Examples of such non-zeolitic phases are polymeric materials and inorganic materials such as glasses, silica or alumina.
Composite membranes or filters of materials such as paper and polymers which may contain dispersed particles of zeolites have been described ,for example, in U.S. Pat. Nos. 3,266,973; 3,791,969; 4,012,206; 4,735,193; 4,740,219 and European Patent Application 254758.
U.S. Pat. No. 4,699,892 describes a composite membrane having an ultrathin film of a cage-shaped zeolite of from 10 to several hundred angstroms in thickness on a porous support of metal, inorganic material or polymeric material.
Non-composited inorganic membranes are described, for example, in U.S. Pat. Nos. 3,392,103; 3,499,537; 3,628,669 and 3,791,969.
U.S. Pat. No. 3,392,103 describes membranes made from hydrous metal oxide ceramics such as aluminum oxide. U.S. Pat. No. 3,499,537 discloses membranes of pressed and sintered aluminum vanadate powder. U.S. Pat. No. 3,628,669 discloses silica membranes made by leaching thin inorganic glass films. U.S. Pat. No. 3,791,969 describes membranes of flocculated sodium exfoliated vermiculite.
Other non-composited membranes described in U.S. Pat. Nos. 3,413,219 and 4,238,590 require some manner of supporting material U S. Pat. No 3,413,219 discloses the preparation of membranes from colloidal hydrous oxide which is formed on a permeable substrate. U.S. Pat. No. 4,238,590 discloses silicic acid heteropolycondensates suitable for use as membranes but which are not self-supporting and are stretched over porous or net-like supporting material
It is therefore an object of the invention to provide a pure and spatially continuous molecular sieve membrane It is also an object to provide a material of macroscopic dimensions, composed only of a zeolitic phase, and having adequate mechanical strength to maintain its macroscopic structural integrity and capable of carrying out molecular sieve action